An analysis of evoked electromyogram from orbicularis oculi in patients with myasthenia gravis.

Summary Evoked electromyograms of the orbicularis oculi muscle with repeated stimulation given at frequencies of 5, 10, 20, 50 and 100 c/s were examined in myasthenia gravis; and the following results were obtained. 1. In the normal subject, the amplitude of M-waves showed almost no change by stimulation at frequencies of 5 and 10 c/s, and a mild gradual increase by stimulation at a frequency of 20 c/s. On stimulation with 50 and 100 c/s, the amplitude of M-waves showed a marked gradual increase and maintained nearly the peak value after a maximum had been reached. 2. In a total of 23 patients with myasthenia gravis, the amplitude of M-waves showed several specific changes against the stimulation frequencies employed. The patterns of the amplitude of M-waves appearing with each frequency were classified into 3 types: Type I, which showed an initial gradual decrease in amplitude with all the stimulation frequencies employed, was observed in 13 patients (56.5%). Type II, which showed an initial gradual decrease at frequencies of 5 c/s and 10 c/s, but a gradual increase followed by gradual decrease at frequencies of 50 and 100 c/s, was observed in 8 patients (34.8%). Type III, which showed no obvious difference from the pattern of the normal curve with stimulation given at not more than 50 c/s but a gradual increase followed by gradual decrease at a frequency of 100c/s, was observed in 2 patients (8.7%). 3. No distinct differences were noted in other neuromuscular diseases taken as control, as compared with the normal.